With the possible exception of the Uchiha, ninja do not wake up one morning and suddenly know a new skill, or jutsu, or ability, or anything. It takes a lot of hard work and dedication to learn to do what ninja do, and isn't something that comes easily, or quickly.
In addition to spending Character Points on jutsu, abilities, skills and fighting styles you must 'training days' to learn and gain new abilities. Every OOC day is one training day, and represents your character's time spent training 'off screen'. The exact amount of training days required is detailed in the CP and Training Cost Chart.
RPing, fighting, sparring, etc do not interrupt training. Nor do most missions. Some things do interrupt training and cause you to 'lose' training days, such as injury, imprisonment, or when a GM declares that training days are lost during an event or mission. You must record *all* training you do. This means the start time, end time, type, and total bonus. If your training is interrupted, you may begin again right where you left off.
'Downtime' passes much faster IC then it does OOC. Downtime means any passage of time not spent in character. Every OOC week is one month in character. Every OOC day is a little over 4 days IC. Time is not consistent, it obviously doesn't pass this fast while you are IC or on a mission. Indeed, time slows and speeds up as is appropriate to further the story and enhance the plot, at the GM's discretion.